SYNTHESIS OF CARBOXYL-REDUCED ANALOGS RELATED TO THE CHLAMYDIA-SPECIFIC KDO TRISACCHARIDE EPITOPE

The disaccharides allyl O-(sodium oxy-alpha-D-manno-2-octulopyranosylo nate)-(2-->4)- 3-deoxy-alpha-D-manno-2-octulopyranoside (8), allyl y-a lpha-D-manno-2-octulopyranosyl)-(2-->8)-(sodium 3-deoxy-alpha-D-manno- 2-octulopyranosidonat (24), and allyl O-(sodium 3-deoxy-alpha )-(2-->8 )-3-deoxy-alpha-D-manno-2-octulopyranoside (35), and the trisaccharide s allyl O-(sodium ha-D-manno-2-octulopyranosylonate)-(2-->8)-(sodium ) -(2-->4)-3-deoxy-alpha-D-manno-2-octulopyranoside (13) and allyl y-alp ha-D-manno-2-octulopyranosyl)-(2-->8)-(sodium ha-D-manno-2-octulopyran osylonate)-(2-->4)-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosidonat e) (30) were prepared. The ketosidic linkages were formed in good yiel ds and high stereoselectivity by BF3.Et(2)O-catalyzed reaction of the per O-acetylated 3-deoxy-alpha-D-manno-2-octulopyranosyl fluoride deri vative (16) with 8-O-SiBu(t)Me(2) derivatives 19 and 21. Coupling reac tions using the Kdo monosaccharide bromide derivative 4 or the alpha-( 2-->8)-linked Kdo disaccharide bromide derivatives 9 and 26 were perfo rmed under Helferich conditions in MeCN or MeNO(2), respectively. The disaccharide halides were prepared in good overall yields starting fro m the readily available allyl beta-glycoside of Kdo. The deprotected o ligosaccharides correspond to the genus-specific lipopolysaccharide ep itope of Chlamydia and part structures thereof, containing the carboxy l-reduced Kdo-residues at the distal and proximal position of the Kdo trisaccharide epitope, respectively.